A survey of benthic invertebrate communities in native and non-native seagrass beds in St. John, USVI

Abstract Halophila stipulacea, a seagrass native to the Indian Ocean, spread to the Caribbean in 2002. Few studies have explored the spatiotemporal distribution of H. stipulacea throughout the Caribbean and whether native invertebrates utilize this non-native seagrass as habitat. We surveyed the shallow, nearshore subtidal zones of four bays in St. John, US Virgin Islands over a two-year period to assess the abundance of both H. stipulacea and native seagrass species. We then surveyed macroinvertebrate communities in one bay with large areas of H. stipulacea, native seagrasses, and bare substrate to assess how macroinvertebrate species composition varied in these habitats. Our survey of the benthic macroinvertebrates revealed that: (1) native invertebrate species utilize H. stipulacea beds and (2) the density and richness of invertebrates was significantly higher in H. stipulacea beds compared to both native seagrass beds and bare substrate. Our results show that H. stipulacea is a common component of nearshore communities in St. John, USVI and that native invertebrates use H. stipulacea beds as habitat — results that agree with findings from other recent studies. While these findings indicate that native macroinvertebrate species can be abundant in non-native seagrass, further investigation, including experimental manipulations, preference tests, and surveys across broad spatial scales, are required to develop a robust understanding of the ecological impacts of this non-native grass.